Method and device for indicating an uncorrectable data block

ABSTRACT

A method and device for indicating an uncorrectable data block. The method includes: if a forward error correction decoding fails, setting synchronization character of at least one of the corresponding data blocks to a first character; and performing line decoding on the data block with the set first character, and outputting decoded data. With the invention, indicating the uncorrectable data block Simple and effective to a line decoding module can be implemented in case of a failure of FEC decoding.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2008/073506, filed on Dec. 15, 2008, which claims priority toChinese Patent Application No. 200810056163.6, filed on Jan. 14, 2008,both of which are hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to optical network communications, inparticular to a method and device for indicating an uncorrectable datablock.

BACKGROUND OF THE INVENTION

The Passive Optical Network (PON) is a point-to-multipoint optical fiberaccess technology, and has advantages such as easy maintenance, broadbandwidth and low cost. The PON is an ideal physical platform foraccessing multiple services such as voice, data and video. The PONincludes an Optical Line Terminal (OLT), an Optical Network Unit (ONU)and an Optical Distribution Network (ODN). Because ODN includes apassive optical splitter/coupler, PON does not require elements havingamplification and relay functions.

The Ethernet Passive Optical Network (EPON) is a PON technique, whichutilizes Ethernet protocols with mature and economical techniques, andhas advantages such as easy maintenance, low cost, broadbandtransmission and better performance-price ratio. In the Ethernetprotocol, a structure of an 802.3 Ethernet data frame corresponding tothe EPON is illustrated in FIG. 1. There is a 4-byte Cyclic RedundancyCheck (CRC) at the end, i.e. before the Extension portion, of each 802.3Ethernet data frame. A receiver can detect certain errors according tothe CRC result.

For improving the anti-jamming capability BER performance of the systemand increasing the power budget of the system, at present the 10G EPONsystem being constituted by the Institute of Electrical and ElectronicsEngineers (IEEE) 802.3av employed forward error control (FEC) codingtechnique. The basic operation of the FEC technique is to add paritycheck bits to the end of a transmitting Ethernet data portion accordingto a predefined rule between the parity check portion and the dataportion. The receiver, on receiving the Ethernet frame from thetransmitter, verifies the association between the Ethernet data portionand the parity check portion of an FEC codeword according to thepredefined rule. If finding the association is incorrect, i.e. the FECdecoding fails, the receiver determines that error occurs during thetransmission of the Ethernet frame and indicates the uncorrectable datablock.

Besides the above FEC coding technique, another coding technique, linecoding is employed at the physical layer of the EPON system. The basicoperation of the line coding is that the original input data isconverted into data in a format that is receivable by the receiver.Meanwhile, the line coding must ensure that there is sufficienttransition that can be provided to a clock recovery circuit. The encoderalso provides a method for aligning data with word, and the line codedsequence can maintain good direct current balance. At present, in the10G EPON system being constituted by the IEEE802.3av workgroup, linecoding mechanisms with higher coding rate such as 64 b/66 b and 64 b/65b are employed. These two line coding mechanisms utilize a scrambler,where the synchronization character and control character of the twoline coding mechanisms bypass the scrambler, i.e. the synchronizationcharacter does not change. According to the 64B/66B coding mechanism, atwo-bit synchronization character (synchronization header) is added onthe basis of 64-bit information. The two-bit synchronization characterhas only two values, “01” and “10”. The synchronization character “01”indicates that all of the 64-bit information is data information, thesynchronization character “10” indicates that the 64-bit informationincludes data information and control information. The synchronizationcharacter “00” or “11” indicates that error occurs during thetransmission. The usage of the synchronization character ensures thatthere is at least one transition at intervals of 66 bits, so as tofacilitate block synchronization. The 64-bit information is scrambledwith an auto-synchronization scrambling mechanism, which can ensure thatthere is sufficient transition for the transmitted data to an utmostextent for facilitating clock recovery. Being different from the 64B/66Bcoding mechanism, the 64B/65B coding utilizes a 1-bit data/controlcharacter. The data/control character “0” indicates that all the 64 bitsare data information. The data/control character “1” indicates the64-bit information includes data information and control information.

For the detection of known error at the Medium Access Control (MAC)layer via CRC verification, a control character /E/ with a length of onebyte, is used in the standard of the IEEE802.3 10G system. The controlcharacter /E/ indicates an error.

A schematic diagram of a corresponding relation between an open systemsinterconnection reference model and an IEEE802.3 10G bit local areanetwork model is illustrated in FIG. 2. At present, the 10G EPON systemconstituted by the IEEE802.3av workgroup utilizes this model, thetransmission rate at the physical layer of which reaches 10 Gbps.

As illustrated in FIG. 2, if the data received from the 10 GIGABIT MEDIAINDEPENDENT INTERFACE (XGMII) by the Reconciliation Sublayer (RS)includes a control character /E/, it indicates that error occurs to thereceived data where the /E/ locates. To ensure that the RS can detectthe error by the CRC checking of the 802.3 Ethernet data frame after thedata arrives at the MAC layer, the RS needs to preprocess the receiveddata. One of processing methods is to replace part of the data so thatthe error can be checked by CRC.

The control character /E/ may be inserted at the transmitting end, or bereplaced at the receiving end. In case of 64/66 b line coding technique,the control character /E/ is received and processed generally in the66/64 b line decoding module of the receiving end. As illustrated inFIG. 3, in the existing IEEE802.3 10 G Ethernet standard, the 66/64 bline decoding module is located at the Physical Coding Sublayer (PCS).

At the physical layer of the existing IEEE802.3 10G Ethernet standard,the 802.3 Ethernet data frame is identified by indicator /S/ and /T/./S/ indicates a start of data frame, and /T/ indicates a termination ofdata frame. The 66/64 b line decoding module determines that erroroccurs to a received data block, if the 66/64 b line decoding module atthe PCS layer of the receiver, after receiving a control character /S/indicating a start of data frame, receives the data block containing asynchronization header “10”, including any control character except acontrol character /T/ indicating a termination of data frame, or if the66/64 b line decoding module at the PCS layer of the receiver receivesan invalid data block having a synchronization header “00” or “11”. Inthis case, the 66/64 b line decoding module replaces all eight bytes inthe data block with control characters /E/. The above /S/, /T/ and /E/have a length of one byte respectively.

The receiver of the 10G EPON system constituted by the IEEE802.3avworkgroup has employed the 66/64 b line decoding module, the XGMII andRS as well as the FEC coding technique at its PCS layer. However, thereis no solution of how to indicate the uncorrectable data block to theline decoding module in the EPON system after the failure of FECdecoding.

SUMMARY OF THE INVENTION

An embodiment of the present invention is to provide a method and devicefor indicating an uncorrectable data block, thereby solving the problemof how to indicate the uncorrectable data block to a line decodingmodule after a failure of FEC decoding.

An object of an embodiment of the present invention is attained by thefollowing technical solution.

A method for indicating an uncorrectable data block, including:

if a forward error correction decoding fails, setting synchronizationcharacter of at least one data block of data of decoding failure to afirst character; and

performing line decoding on the data block containing the firstcharacter, and outputting decoded data.

A device for indicating an uncorrectable data block includes:

a first character setting module, adapted to perform forward errorcorrection decoding, and if a failure of the forward error correctiondecoding is detected, set synchronization character of at least one datablock of data of decoding failure to a first character;

a line decoding module, adapted to perform line decoding on the datablock containing the first character, and outputting decoded data.

It can be seen from the technical solution of embodiments of the presentinvention, by setting synchronization characters of part or all of datablocks (Blocks) of error data by detecting a failed FEC decoding (dataportion of an FEC codeword) to a first character, error occurrence tothe data blocks can be determined by the line decoding module accordingto the line decoding rule and the first character.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural diagram of an 802.3 Ethernet data framecorresponding to EPON in an Ethernet protocol;

FIG. 2 illustrates a relation between an open systems interconnectionreference model and an IEEE802.3 10G bit local area network model;

FIG. 3 illustrates the location of the 66/64 b line decoding module atthe receiving end in the IEEE802.3 10G standard;

FIG. 4 is a structural diagram of an FEC codeword in the 10G EPON systemaccording to a first embodiment of the present invention;

FIG. 5 is a structural diagram of the receiver in the 10G EPON systemaccording to the first embodiment of the present invention;

FIG. 6 is a flowchart of indicating an uncorrectable data block at thereceiver of the 10G EPON after detecting failure of FEC decodingaccording to the first embodiment of the present invention;

FIG. 7 is a data structure diagram of an FEC codeword after thesynchronization header of any block of the data portion of the FECcodeword is set to “00” or “11” according to the first embodiment of thepresent invention;

FIG. 8 is a data structure diagram of an FEC codeword aftersynchronization headers of any blocks of the data portion of the FECcodeword are set to “00” or “11” according to the first embodiment ofthe present invention;

FIG. 9 is a data structure diagram of an FEC synchronization headers ofthe first and last blocks of the data portion of the FEC codeword areset to “10” according to the first embodiment of the present invention;

FIG. 10 is another data structure diagram of an FEC synchronizationheaders of the first and last blocks of the data portion of the FECcodeword are set to “10” according to the first embodiment of thepresent invention;

FIG. 11 is a data structure diagram of an FEC codeword aftersynchronization headers of multiple blocks including the first and lastblocks of the data portion of the FEC codeword are set to “10” accordingto the first embodiment of the present invention;

FIG. 12 is another data structure diagram of an FEC codeword aftersynchronization headers of multiple blocks including the first and lastblocks of the data portion of the FEC codeword are set to “10” accordingto the first embodiment of the present invention;

FIG. 13 is a data structure diagram of the synchronization header of anyblock of the data portion of the FEC codeword is set to “00” or “11”according to a second embodiment of the present invention;

FIG. 14 is a data structure diagram of an FEC codeword aftersynchronization headers of any blocks of the data portion of the FECcodeword are set to “00” or “11” according to the second embodiment ofthe present invention;

FIG. 15 is a data structure diagram of an FEC codeword aftersynchronization headers of the first and last blocks of the data portionof the FEC codeword are set to “10” according to the second embodimentof the present invention;

FIG. 16 is another data structure diagram of an FEC codeword aftersynchronization headers of multiple blocks including the first and lastblocks of data portion of the FEC codeword are set to “10” according tothe second embodiment of the present invention;

FIG. 17 is a data structure diagram of an FEC codeword aftersynchronization headers of the first and last blocks of the data portionof the FEC codeword are set to “1” according to a third embodiment ofthe present invention;

FIG. 18 is another data structure diagram of an FEC codeword aftersynchronization headers of multiple blocks including the first and lastblocks of the data portion of the FEC codeword are set to “1” accordingto the third embodiment of the present invention; and

FIG. 19 is a structural diagram of a device for indicating anuncorrectable data block according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

In an embodiment of the present invention, the error data is obtainedafter an FEC decoding failure of an FEC codeword. The error data is thedata portion of the FEC codeword prior to the FEC decoding that includesmultiple blocks, each of which including a synchronization header anddata information. Then, the synchronization characters of part or all ofblocks of the error data are set to first characters.

If a 64/66 b line coding is applied to the blocks, the first characteris “11”, “00” or “10”. In practical application, synchronizationcharacters of any one or more blocks of data portion of the FEC codewordmay be set to at least one of the values of “11”, “00” and “10”. Forexample, synchronization characters of any one or more blocks of thedata portion of the FEC codeword can be directly set to at least one of“11” and “00”. In another example, synchronization characters of thefirst and last blocks or multiple blocks including the first and lastblocks of the data portion of the FEC codeword can be set to “10”. In afurther example, synchronization characters of any one or more blocks ofthe data portion of the FEC codeword are directly set to “10”, and thesynchronization characters of at least one of the rest blocks aredirectly set to at least one of “11” and “00”.

If a 64/65 b line coding is applied to the blocks, the first characteris set to “1”. In practical application, synchronization characters ofthe first and last blocks or multiple blocks including the first andlast blocks of the data portion of the FEC codeword may be set to “1”.

Then, each block is input to the descrambler, the data information ofthe block changes, but synchronization header bits of the block bypassthe descrambler such that the synchronization header bits do not change.Each descrambled block including the synchronization header anddescrambled data information is then sent to a line decoder. The linedecoder detects errors within part or all of blocks according to thesynchronization characters of part or all of the blocks having a valueof “11” or “00” or according to the synchronization characters of a partor all of the blocks having a value of “10” or “1” but controlcharacters included in the part or all of the blocks do not conform witha line decoding rule. The line decoder replaces the descrambled data ofthe part or all of the blocks, and outputs the decoded data.

Embodiments of the present invention are described in detail withreference to the attached drawings.

A first embodiment of the present invention: This embodiment provides amethod for setting the synchronization header of a data block of errordata once FEC decoding fails, if a 64/66 b line code is employed at thephysical layer of the 10G EPON system and only the second bit of thesynchronization header involves in the FEC coding,

In this embodiment, a structure of an FEC codeword with the FEC codingand the 64/66 b line coding is illustrated in FIG. 4, in which theformer m Blocks (data units) are 802.3 Ethernet data, and the latterblocks are parity check blocks. If RS (255, 223) coding is adopted, m=27and n=4.

During the data receiving process, i.e. after a control character /S/indicating a start of data frame is identified and if the FEC decodingfails, synchronization headers of part or all of blocks of the dataportion of the FEC codeword as illustrated in FIG. 4 are set to acontrol synchronization character “10” or an invalid synchronizationheader “00” or “11”, in order to indicate the uncorrectable data block.

A structural diagram of a receiving end in the 10G EPON system accordingto this embodiment is illustrated in FIG. 5. A flowchart of indicatingan uncorrectable data block at the receiver in case of an FEC decodingfailure is illustrated in FIG. 6. In the process, after thesynchronization of the received blocks, the blocks are first sent to thebuffer of the FEC decoding module. Because the first synchronizationheader bit of the data portion blocks and all synchronization headerbits of the parity check portion blocks do not involve in FEC coding,the FEC decoding module removes the synchronization header bits of theblocks which do not involve in the FEC coding so as to form another FECcodeword in another format corresponding to the encoding, and input theFEC codeword in the another format to the FEC decoding module forperforming FEC decoding.

The FEC decoding module performs decoding on the FEC codeword in theformat corresponding to the encoding. The synchronization headers ofpart of the blocks in the FEC codeword are set to “10”, “00” or “11”after an FEC decoding failure.

Methods for setting the synchronization header according to thisembodiment are described as follows:

If the synchronization header can be set to “00” or “11”, two methodsare provided: the first method is to set the first synchronizationheader bit to be the same as the second synchronization header bit inthe synchronization header recovery process; the second method is to setthe synchronization header bits to “00” or “11” directly in thesynchronization header recovery process.

If the synchronization header is set to “00” or “11”, two methods areprovided: the first method is to set the second bit of thesynchronization header, output from the FEC decoding module, to “0” or“1” corresponding to either of “00” and “11” as designated, then thefirst synchronization header bit is set to be the same as the secondsynchronization header bit in the synchronization header recoveryprocess; the second method is to set the synchronization header bits to“00” or “11” directly as designated in the synchronization headerrecovery process.

During the above operations on the synchronization header, only thesynchronization header of any block of the data portion of the FECcodeword may be set, the resulted first bit is set to the same as thesecond bit, i.e. SH[0]=SH[1]. SH[0] represents the first bit of thesynchronization header, and SHE represents the second bit of thesynchronization header. With the above operations, the synchronizationheader after recovery is “00” or “11”. A structural diagram of the FECcodeword after the synchronization header of any block of the dataportion of the FEC codeword is set is illustrated in FIG. 7.

Alternatively, during the above operations on the synchronizationheader, only synchronization headers of any blocks of data portion ofthe FEC codeword may be set, the resulted first bit is set to the sameas the second bit, i.e. SH[0]=SH[1]. A structural diagram of the FECcodeword after synchronization headers of any Blocks of data portion ofthe FEC codeword are set is illustrated in FIG. 8.

If the synchronization header is set to “10”, two methods are provided:the first method is to set the second bit or the first bit of asynchronization header to “0” or “1” respectively after the FECdecoding, if that bit of the synchronization header involves in the FECcoding, then a synchronization header default inversion recoverymechanism is adopted to recover a synchronization header “10” in asynchronization header recovery; the second method is to set thesynchronization header bits to “10” directly in the synchronizationheader recovery process after the FEC decoding.

During the above operations on the synchronization header, onlysynchronization headers of the first and the last blocks of the dataportion of the FEC codeword may be set. A structural diagram of dataportion of the FEC codeword after the setting is illustrated in FIG. 9if the first method is adopted. A structural diagram of data portion ofthe FEC codeword after the setting is illustrated in FIG. 10 if thesecond method is adopted.

Alternatively, during the above operations on the synchronizationheader, the synchronization headers of multiple blocks including thefirst and the last blocks of data portion of the FEC codeword may beset. A structural diagram of data portion of the FEC codeword isillustrated in FIG. 11 if the first method is adopted. A structuraldiagram of data portion of the FEC codeword is illustrated in FIG. 12 ifthe second method is adopted.

A second embodiment: This embodiment provides, if a 64/66 b line codingis employed at the physical layer of the 100 EPON system and two bits ofthe synchronization header involve in an FEC coding, a method forsetting the synchronization header of a data block once there is an FECdecoding failure.

Because two bits of the synchronization header involve in the FECcoding, the synchronization header recovery process is not required andthe setting of synchronization header can be performed in the FECdecoding module. If the FEC decoding fails, in order to indicate thaterror occurs, synchronization headers of part of blocks of the FECcodeword as illustrated in FIG. 4 are set to a control blocksynchronization header “10” or an invalid synchronization header “00” or“11”, for indicating the uncorrectable data block.

Methods for setting a synchronization header according to thisembodiment are described as follows.

If the synchronization header is to be set to “00” or “11”, the FECdecoding module may set the synchronization header of any data portionblock of the FEC codeword to “00” or “11”, i.e. SH=00 or SH=11. A datastructure of the FEC decoding output after the setting is illustrated inFIG. 13. Alternatively, the FEC decoding module may set thesynchronization headers of any data portion blocks to “00” or “11”, i.e.SH=00 or SH=11. A data structure of the FEC decoding output after thesetting is illustrated in FIG. 14.

If the synchronization header is to be set to “10”. The FEC decodingmodule may set the synchronization headers of the first and the lastdata portion blocks of the FEC codeword to “10”, i.e. SH=10, so that itcould set /E/ correctly even if the blocks include the terminationcontrol character /T/ or the start control character /S/. A datastructure of the FEC decoding output after the setting is illustrated inFIG. 15. Alternatively, the FEC decoding module may set synchronizationheaders of multiple blocks including the first and last data portionblocks of the FEC codeword to “10”, i.e. SH=10. A data structure of theFEC decoding output after the setting is illustrated in FIG. 16.

A third embodiment: This embodiment provides a method for setting asynchronization header once an FEC decoding fails if a 64/65 b linecoding is employed at the physical layer and two bits of thesynchronization header involve in the FEC coding,

In the case of 64/65 b line coding, the synchronization header is in theform of only “0” or “1”, where “0” indicates that 64 bits are all datainformation, and “1” indicates that 64 bits includes data informationand control information. Therefore, only “1” may be used to setsynchronization header to indicate the uncorrectable data block once theFEC decoding fails.

In order to avoid the fact that the 65/64 b line decoding module can notproperly replace the data block of the error data, due to FEC decodingfailure, with /E/, which is in the location of the termination controlcharacter /T/ or the start control character /S/, a method for settingthe synchronization header according to this embodiment is described asfollows.

The FEC decoding module sets the synchronization headers of the firstand last data portion blocks of the FEC codeword to “1”, i.e. SH=1. Adata structure of the FEC decoding module output after the setting isillustrated in FIG. 17. The FEC decoding module sets synchronizationheaders of any blocks including the first and last data portion blocksof the FEC codeword to “1”, i.e. SH=1. A data structure of the FECdecoding output after the setting is illustrated in FIG. 18.

Preferably, taking the blocks as input, the data portion of the FECcodeword after the above operations to the synchronization headers issent to a descrambler, the data information bits of the blocks arechanged but the synchronization headers of the blocks bypass thedescrambler. The data portion of the original FEC codeword after thedescrambled is sent to a line decoding module. If the 64/66 b linecoding is adopted, the line decoder detects errors within part or all ofthe blocks in accordance with the synchronization characters having avalue of “11” or “00”; or in accordance with the synchronizationcharacters of part or all of the blocks having a value of “10” but theblocks do not conform with the 64/66 b line decoding rule.

If the 64/65 b line coding is adopted, the line decoder detects errorswithin part or all of the blocks in accordance with the synchronizationcharacters of the part or all of the blocks of the FEC codeword having avalue of “1” but the part or all of blocks do not conform with the 64/65b line decoding rule.

As a result, the line decoding module replaces part or all blocks with/E/ by replacing all eight bytes of each block with /E/, therebyindicating the uncorrectable data block by utilizing /E/, so that theMAC layer can detect the error via its own CRC verification.

A structure of a device for indicating an uncorrectable data blockaccording to an embodiment of the present invention is illustrated inFIG. 19. The device includes a first character setting module and a linedecoding module, and may further include a descrambling module.

A first character setting module, adapted to perform forward errorcorrection decoding, and if a failure of the forward error correctiondecoding is detected, set synchronization character of at least one datablock of data of decoding failure to a first character. The firstcharacter is an illegal synchronization character specified in a linecoding rule of decoding each block, or a synchronization character of adata block including control information. The first character settingmodule includes at least one of an illegal character setting module anda control character setting module.

The descrambling module is adapted to descramble data information ofeach block containing the first character before the line decodingmodule decodes the data block containing the first character.

The line decoding module is adapted to perform line decoding on theblocks containing the first character and output the decoded data. Alsothe line decoding module detects error within the data block containingthe first character according to a predefined line coding rule and thefirst character, and replaces the descrambled data information in thedata block. The line decoding module includes at least one of a firstdecoding module and a second decoding module.

The first character setting module may include an illegal charactersetting module, which is adapted to set the synchronization charactersof part or all of blocks with error to the illegal synchronizationcharacter specified in the line coding rule. In the case of a 64/66 bline coding, the illegal character is “11” or “00”.

The first character setting module may further include a controlcharacter setting module, which is adapted to set synchronizationcharacters of part or all of data blocks of the error data to asynchronization character of a data block including control information.In the case of a 64/66 b line coding, the synchronization character isto be set to “10”. In the case of a 64/65 b line coding, thesynchronization character is to be set to “1”.

The first character setting module may include both of the illegalcharacter setting module and the control character setting module.

The line decoding module may include the first decoding module, which isadapted to determine part or all of data blocks of the error data withillegal synchronization characters, replace the descrambled datainformation of the part or all of data blocks, then output the replaceddata; or determine part or all of data blocks of the error data withlegal synchronization characters and perform line decoding on the partor all of blocks, then output decoded blocks.

The line decoding module may include the second decoding module, whichis adapted to determine part or all of data blocks of the error datawith synchronization characters of the data blocks containing controlinformation (i.e. “10” or “1”); if the part or all of data blocks do notconform with the line coding rule, replace the descrambled datainformation of the part or all of data blocks, and output the replaceddata; if the part or all of data blocks conform with the line codingrule, perform line decoding on the part or all of the data blocks andoutput the decoded data, respectively.

In another embodiment, the first decoding module is adapted to replacethe descrambled data of the part or all of data blocks, perform linedecoding on the part or all of data blocks, and output the replaceddata, after the first decoding module determines the part or all of datablocks of the error data with illegal synchronization characters;

the second decoding module is adapted to replace the descrambled data ofthe part or all of data blocks, perform line decoding on the part or allof data blocks, and output the decoded data, after the second decodingmodule determines the part or all of data blocks of the error data withsynchronization characters of the data blocks containing controlinformation.

The line decoding module may include both of the first decoding moduleand the second decoding module.

As described above, the embodiment of the present invention provides aneasy and effective mechanism for indicating the uncorrectable data blockto the line decoding module in the case of failure of FEC decoding.Therefore, the line decoding module can utilize the existing errorreport function of the control character /E/ of the Ethernet system toreport error to the RS layer where the error data can be preprocessed,so that the MAC layer can detect the error via its own CRC verification.

The above description is merely for preferred detailed embodiments ofthe present invention, which the protective scope of the presentinvention is not limited to. Any modifications and settings that can beeasily made by those skilled in the art within the disclosure of thepresent invention should fall within the scope of the present invention.Therefore, the protective scope of the present invention should bedefined as the claims.

1. A method for indicating an uncorrectable data block, comprising: if aforward error correction decoding fails, setting synchronizationcharacter of at least one data block of data of decoding failure to afirst character; and performing line decoding on a data block whichcontain the first character, and outputting decoded data.
 2. The methodfor indicating an uncorrectable data block according to claim 1, furthercomprising: performing forward error correction decoding on receiveddata, and determining a failure of forward error control, FEC, decoding.3. The method for indicating an uncorrectable data block according toclaim 1, further comprising: descrambling the data block which containsthe first character prior to line decoding.
 4. The method for indicatingan uncorrectable data block according to claim 3, wherein the firstcharacter is an illegal synchronization character specified by a linecoding, or a synchronization character which indicates controlinformation.
 5. The method for indicating an uncorrectable data blockaccording to claim 1, wherein the process of setting synchronizationcharacter of at least one data block of the error data to a firstcharacter comprises: if a 64/66 b line coding is adopted, settingsynchronization characters of part or all of the data blocks of theerror data to at least one of “11”, “00” and “10”.
 6. The method forindicating an uncorrectable data block according to claim 5, wherein theprocess of setting synchronization characters of part or all of the datablocks of the error data to at least one of “11”, “00” and “10”comprises: setting synchronization characters of any one or more of datablocks of the error data to at least one of “11” and “00”.
 7. The methodfor indicating an uncorrectable data block according to claim 5, whereinthe process of setting synchronization characters of part or all of thedata blocks of the error data to at least one of “11”, “00” and “10”comprises: setting synchronization characters of any one or more of datablocks of the error data to “10”; setting synchronization character ofone or more of the rest data blocks to at least one of “11” and “00”; orperforming a synchronization character recovery on the data blocks ofthe error data so that two bits of synchronization characters of any oneor more of data blocks of the error data have the same value; or settingvalues of bits involving in the forward error correction coding insynchronization characters of any one or more of data blocks of theerror data to “1” or “0” as designated, performing a synchronizationcharacter recovery on the corresponding data blocks so that the two bitsof the synchronization characters of the any one or more of data blockshave the same value; or setting synchronization characters of the firstand last data blocks or multiple data blocks including the first andlast data blocks of the error data to “10”.
 8. The method for indicatingan uncorrectable data block according to claim 5, wherein the process ofsetting synchronization characters of part or all of the data blocks ofthe error data to at least one of “11”, “00” and “10” comprises: settinga value of a first bit involving in the forward error correction codingin synchronization characters of the first and last data blocks ormultiple data blocks including the first and last data blocks of theerror data to “1”, performing a synchronization character inversionrecovery on the first and last data blocks or the multiple data blocksincluding the first and last data blocks, so that a second bit of thefirst and last data blocks or the multiple data blocks including thefirst and last data blocks has an inverse value of the first bit; orsetting a value of a second bit involving in the forward errorcorrection coding in synchronization characters of the first and lastdata blocks or multiple data blocks including the first and last datablocks of the error data to “0”, performing a synchronization characterinversion recovery on the first and last data blocks or the multipledata blocks including the first and last data blocks, so that a firstbit of the first and last data blocks or the multiple data blocksincluding the first and last data blocks has an inverse value of thesecond bit.
 9. The method for indicating an uncorrectable data blockaccording to claim 4, wherein the process of setting synchronizationcharacter of at least one data block to a first character comprises: ifa 64/65 b line coding is adopted, setting synchronization characters ofpart or all of data blocks of the error data to “1”.
 10. The method forindicating an uncorrectable data block according to claim 9, wherein theprocess of setting synchronization characters of part or all of datablocks of the error data to “1” comprises: setting synchronizationcharacters of the first and last data blocks or multiple data blocksincluding the first and last data blocks to “1”.
 11. The method forindicating an uncorrectable data block according to claim 5, wherein theprocess of performing line decoding on the data block containing thefirst character, and outputting the decoded data comprises: afterknowing that the synchronization characters of the part or all of datablocks of the error data are “11” or “00”, replacing the descrambleddata of the part or all of data blocks, and outputting the replaceddata.
 12. The method for indicating an uncorrectable data blockaccording to claim 5, wherein the process of performing line decoding onthe data block containing the first character, and outputting thedecoded data comprises:after knowing that the synchronization charactersof the part or all of data blocks of the error data are “10” and thepart or all of data blocks do not conform with the line decoding rule,replacing the descrambled data of the part or all of data blocks, andoutputting the replaced data.
 13. The method for indicating anuncorrectable data block according to claim 9, wherein the process ofperforming line decoding on the data block containing the firstcharacter, and outputting decoded data comprises: after knowing that thesynchronization characters of the part or all of data blocks of theerror data are “1” and the part or all of data blocks do not conformwith the line decoding rule, replacing the descrambled data of the partor all of data blocks, and outputting the replaced data.
 14. A devicefor indicating an uncorrectable data block, comprising: a firstcharacter setting module, adapted to perform forward error correctiondecoding, and if a failure of the forward error correction decoding isdetected, set synchronization character of at least one data block ofdata of decoding failure to a first character; and a line decodingmodule, adapted to perform line decoding on the data block containingthe first character, and outputting decoded data.
 15. The device forindicating an uncorrectable data block according to claim 14, furthercomprising: a descrambling module, descramble the data block containingthe first character before the line decoding module performs linedecoding on the data block containing the first character.
 16. Thedevice for indicating an uncorrectable data block according to claim 15,wherein the first character setting module comprises at least one of anillegal character setting module and a control character setting module;the illegal character setting module is adapted to set synchronizationcharacters of a part or all of data blocks of the error data to anillegal synchronization character specified in a line decoding rule; thecontrol character setting module is adapted to set synchronizationcharacters of a part or all of data blocks of the error data to asynchronization character of a data block containing controlinformation.
 17. The device for indicating an uncorrectable data blockaccording to claim 16, wherein the line decoding module comprises atleast one of a first decoding module and a second decoding module; thefirst decoding module is adapted to replace the descrambled data of thepart or all of data blocks, perform line decoding on the part or all ofdata blocks, and output the replaced data, after the first decodingmodule determines the part or all of data blocks of the error data withillegal synchronization characters; the second decoding module isadapted to replace the descrambled data of the part or all of datablocks, perform line decoding on the part or all of data blocks, andoutput the decoded data, after the second decoding module determines thepart or all of data blocks of the error data with synchronizationcharacters of the data blocks containing control information.